welded connections
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Welded ConnectionsTRANSCRIPT
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Lecture Notes #8Welded Connections
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Professor Guowei MaOffice: 160
Tel: 61-8-6488-3102Email: [email protected]
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Weld Design Standards
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• AS/NZS 1554.1: Structural steel welding ‐Welding of steel structures
• AS 1554.2: Structural steel welding ‐ Stud welding (steel studs to steel)
• AS/NZS 1554.5: Structural steel welding ‐Welding of steel structures subject to high levels of fatigue loading
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Welded Connections• Fabrication
• Field work
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Compounding of sections
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Welded Connections
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Intermediate web stiffeners
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Weld Symbols
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Failure Modes of Welded Joints
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• Ductile fracture at a nominal stress in the vicinity of the
ultimate strength of the weld metal or the parent metal,
whichever is the lower
• Brittle fracture at a nominal stress lower than ultimate
strength and sometimes lower than the working stress
• Progressive fracturing by fatigue after a certain number of
stress cycles
• Other causes such as corrosion, corrosion fatigue, stress
corrosion and creep, but these are relatively rare in steel
structures
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Design Requirement
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(a) The parent material must be ductile, or notch‐tough, at the
service temperature intended and for the thickness required
(b) The details of joints must be such that stress concentrations
are minimized
(c) Reduction of ductility by triaxial stressing should be avoided
at critical joints
(d) Weld defects should be below the specified maximum size
(e) Welded fabrication should not substantially alter material
properties.
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Selection of Weld Type
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• Butt splices, lap splices, T‐joints, cruciform and corner joints
• Butt, fillet or compound
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Lamellar Tearing
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Butt Welds
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Weld defects in butt weld
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Butt Welds
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Plate edge preparation for butt weld
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Fillet Welds
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Longitudinal fillet weld
Transverse fillet weld
Intermittent fillet weld
Plug and slot weld
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Fillet Welds
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Typical weld defect in fillet weld
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Compound Welds
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Hybrid of a fillet and butt weld:former weld type is superimposed onto the latter
Design throat thickness (DTT)The design throat thickness (tt) of a weld is the minimum distance from the root of a weld to its face, less any reinforcement
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Design of Butt Welds
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Complete penetration butt weld—a butt weld in which
fusion exists between the weld and parent metal
throughout the complete depth of the joint.
Incomplete penetration butt weld—a butt weld in which
fusion exists over less than the complete depth of the
joint.
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CPBW
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Clause 9.7.2.7(a) of AS 4100 notes that the design capacity of a
CPBW is equal to the nominal capacity of the weakest part being
joined multiplied by a capacity reduction factor, φ, which is
commensurate with the weld quality. From Table 3.4 of AS 4100
φ = 0.9 for CPBW with SP quality and φ = 0.6 for CPBW with GP
quality. This applies to CBPW subject to transverse and shear
loads.
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Based on the above, for two similar plates joined by a CPBW
with SP quality (φ=0.9) welded to AS/NZS 1554.1 or AS/NZS
1554.5, the AS 4100 definition notes that the weld is as strong
as the joined plate elements and no further calculation is
required (if the plates have been already sized for the design
loads). If the lower quality GP category is used instead of the SP
category for this connection type (i.e. with φ = 0.6), the CPBW
will have a lower design capacity than each of the two similar
connected plates by a factor of (0.6/0.9=) 0.667.
CPBW
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IPBW
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As the weld fusion in a IPBW does not cover the full depth of
the joint, Clause 9.7.2.7(b) of AS 4100 states that IPBW are to
be designed as fillet welds (see Section 8.7.2). The capacity
reduction factor, φ, for IPBW is the same as that for fillet
welds.
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Design of Fillet Joint
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Design of Fillet Joint
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Capacity of a fillet weld
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Φ: 0.8 (for SP quality welds); 0.6 (for GP quality welds)0.7 (for SP category longitudinal welds to RHS with t 3mm)
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Minimum Size of a Fillet Weld
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Design capacities of equal‐leg fillet welds (in kN per 1 mm weld length)
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Along an Edge
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Analysis of weld groups
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(a) The welds are regarded as homogeneous, isotropic and
elastic elements.
(b) The parts connected by welding are assumed to be rigid, but
this assumption should not be made if there is doubt about
the rigidity of adjoining plates.
(c) The effects of residual stresses, stress concentration and
triaxial stress conditions are neglected on the assumption
that the ultimate strength of weld groups is not significantly
affected by these parameters.
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Capacity reduction factors, φ, for welds
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In‐Plane Load
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Out‐of‐Plane Load
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Out‐of‐Plane Load
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Alternative procedure
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Out‐of‐Plane Load
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Alternative procedure
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Design Connections as Whole
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Design Connections as Whole
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• Beam flange weld capacity
• Beam web weld capacity
• Column web capacity in bearing (crushing)
• Column flange capacity at beam tension flange region
• Column web capacity in shear yielding and shear buckling
• Column web capacity in compressive buckling
• Other checks
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Design Connections as Whole
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